Abstract:

Abstract:Aiming at the problem of initial damage and fatigue damage for polymer bonded explosive (PBX), the nonlinear ultrasonic parameters of two kinds of triamino trintrobenzene(TATB)-based PBX cylindrical specimens with different density formed by compression molding and these specimens in the process of compressive fatigue were tested by self-established nonlinear ultrasonic testing device. The nonlinear ultrasonic testing results were verified by fracture surface analysis and computer tomography (CT) testing. Compared with TATB-based PBX specimens with less initial interfacial micro-damage degree, the nonlinear ultrasonic coefficients of the TATB-based PBX specimens with obvious interfacial damage are obviously higher. There is a certain relevance between the nonlinear ultrasonic coefficient and the initial damage degree of TATB-based PBX. When the microscopic crack is nearly generated in the TATB-based PBX, the nonlinear ultrasonic coefficient increases sharply and reaches maximum, revealing that the nonlinear ultrasonic parameters can monitor the fatigue damage developing process. There is a certain difference in fatigue damage rate and developing process for TATB-based PBX specimens with different initial micro-damage degree.

Abstract:To obtain the effects of mass fraction of carbon black and environmental pressure on the ignition and combustion performance of polyethylene, the solid fuel samples with different composition ratio were processed, their ignition and combustion characteristics were investigated by using a CO₂ laser as the ignition source. The experimental process was recorded with a high speed camera. The surface morphology of solid fuels after combustion were examined using scanning electron microscope. The ignition and combustion processes, ignition delay time and burning rate of solid fuel samples with different composition ratio at different environment pressures were analyzed. Results show that the ignition process of solid fuel polyethylene is a typical gas phase ignition and combustion flame is a diffusion flame. The ignition delay time shortens sharply with the addition of carbon black, when the mass fraction of carbon black is higher than 20%, the effect of increase of mass fraction of carbon black on ignition delay time is very small. The ignition delay time shortens with the increase of environment pressure, when the environment pressure is higher than 0.2 MPa, the effect of increase of environment pressure on ignition delay time also is very small. According to the experimental results, when the environment pressure is 0.1, 0.2, 0.3, 0.4, 0.5 MPa, the function relationship between ignition delay time and mass fraction of carbon black is fitted and obtained by using the least squares method. The burning rate of solid fuels decreases with the increase of mass fraction of carbon black, and increases with the increase of environmental pressure. The mass fraction of carbon black is the main factor affecting the burning rate of solid fuels when the mass fraction of carbon black is higher than 5%.

Abstract:The range and longitudinal intensity of base-bleed projectile are closely related to the working performance of igniter. The combustion expansion characteristics of igniter with different orifice diameters(6.5, 8 mm) for five kinds of ignition agents, magnesium/polytetrafluoroethylene (MT) (Mg/PTFE 45/55, Mg/PTFE 55/45, Mg/PTFE 61/39), barium nitrate (Ba (NO₃)₂) and zirconium hydride/lead oxide (ZrH₂/PbO₂ 40/60), were investigated in the atmospheric environment by using high-speed camera system and infrared thermal imager and then the flame temperature field distribution of seven kinds of igniters was measured. On the basis of experiment, the cell-centered finite volume method based on internal nodes was applied to three-dimensional numerical simulation of the combustion jet field of MT igniter. The distribution rule of combustion characteristic parameters of the igniter in the atmosphere under different mass ratios of MT and orifice diameters of the igniter was analyzed. The experimental and numerical results show that ZrH₂/PbO₂ igniter will destroy the "parallel layer" combustion law of base bleed propellant. The ignition area effective factor is proposed to represent the significant degree of the propellant ignition area, and is combined with the ignition time to synthetically evaluate the ignition performance of the igniter. It is found that the MT igniter with mass ratio of 61:39 and orifice diameter of 8 mm is the best. The maximum flame temperature region of igniter is located above the potential core of the nozzle. The smaller the magnesium content in the range of 0.45-0.61 is, the higher the flame temperature in the combustion field of the MT igniter. When the magnesium content is constant and the orifice diameter of igniter is 6.5 mm and 8 mm, the larger orifice diameter has the stronger heat convection in the combustion field, the higher center axial temperature and the greater temperature gradient.

Abstract:Two kinds(casting moulding and pressed fitting) of HMX-based anti-overloaded explosives were chosen to study the damage characteristics and damage failure mechanisms of explosives under overloaded conditions by shock loading. The shock damage was conducted based on shock wave sensitivity test. The damage characteristics of samples before and after shock loading were studied by CT and the shock wave sensitivity was also tested after damage. Results of CT test show that no macro-damage appear in explosive by pressed fitting after the shock damage, while a cavity with length of 7-8 mm and diameter of 1-2 mm appears in cast explosive and is located at 7-8 mm away from one end of the witness board. After shock damage experiments, for cast explosive, above the position of 40 mm from the bottom surface, the explosive density decrease by 1%-5%, and for the pressed fitting explosive, above the position of 50 mm from the bottom surface, the explosive density increase by 1%-8%. The shock wave sensitivity of the both samples decreases after shock damage. The critical gap thicknesses of the cast explosive decreases from 25-27 mm before damaged to 13-15 mm after damaged, while for pressed fitting explosive, the thickness decrease from 38-40 mm to 30-32 mm.

Abstract:To study the effect of initial damages on the structural change and damage behavior of polymer bonded explosive (PBX) under external force, the initial damages was simulated by the way of prefabricated defects, three groups of simulated material samples of PBX, including the sample without prefabricated defect, sample with oblique 45° non-through defect and sample with oblique 45° through defect were prepared, in-situ studies were performed on X-ray CT system. using the loading way of improved arc compress head Brazilian test. Information on three dimensional morphology, size and spatial distribution of cracks and pores were obtained by digital image processing techniques.The finite element simulation of the test was carried out by using ABAQUS software. Results show that when the prefabricated defect has a certain angle to the loading direction of Brazilian test, the prefabricated defect makes the symmetry of its loadig way destroy and the damage behavior of the sample will also change accordingly. The influence of non-through defects and through defects on the damage behavior of samples is very different, the non-through defect may result in stratification phenomenon of the sample. namely the effect of surface defects on the damage behavior of the samples is mainly concentrated in the defective part. The simulation results are in good agreement with the experimental, and explaine the experimental phenomena to some extent.

Abstract:To explore the method of controlling the combustion stability of bulk-loaded propellant guns, the multi-structure cylindrical and cylindrical stepped-wall type observation chambers were designed to analyze the expansion processes of four combustion-gas jets by the high-speed digital recording system. The average axial displacements of the combustion-gas jet head at different times were obtained by processing the sequence diagrams of the jet expansion process. and the effects of A-type, B-type and G-type observation chambers with different expanding ratios and different jet pressures, nozzle diameters and nozzle center interval etc. parameters in A-type observation chamber on the expansion characteristics of four combustion-gas jet in liquid medium were compared. The experimental results show that the stepped-wall type structure can enhance the radial disturbance of the jet due to the induction of the step. When the expanding ratio ΔD/L increases from 0.3 to 0.6, the axial displacement of the jet decreases by 10.8%. With increasing the injection pressure, the gas jet intensity increases. When the injection pressure increases from 9.18 MPa to 15.30 MPa, jet axial displacement increases by 20.9% at 4 ms. When the nozzle diameter increases from 1.4 mm to 2.0 mm, the gas-liquid mixing is more intense, and the jet axial displacement increases by 24.1% at 5 ms. Increasing the nozzle center interval can make the radial expansion more fully and reduce the axial expansion process. When the nozzle center interval increases from 16 mm to 20 mm, the axial displacement reduces by 20.6% at 5 ms.

Abstract:To investigate the action mechanism of combustion chamber geometries on the stabilities of combustion and propulsion processes of bulk-loaded energetic liquid, based on theory of hydrodynamics and component transport equation, a two-dimensional axisymmetric model for gas-liquid two-phase flow and combustion was established. Numerical simulations for the chemical reaction flow fields in the cylindrical and multi-stage stepped-wall combustion chambers were conducted. The distribution characteristics of temperature, velocity, pressure, as well as volume fraction were studied via tracking of the expansion of gas cavity and movement of burning surface. The influence rule of combustion chamber geometries on the evolution processes of flow fields was analyzed. Results show that gas cavity formed after ignition and combustion of energetic liquid expands rapidly in the liquid, when the combustion gas cavity penetrates the liquid and develops to projectile bottom, the burning surface along the axial of the combustion chamber grows rapidly, the Kelvin-Helmholtz′s instability effect occurs due to the tangential velocity difference between gas and liquid, whereas stepped-wall combustion chamber is helpful for inducing radial turbulence, slowing the axial expansion velocity of gas cavity, suppressing axial Kelvin-Helmholtz′s instability effect, and enhancing the stabilities of the combustion and propulsion processes of bulk-loaded energetic liquid. The calculated results are in good agreement with the experimental data.

Abstract:To reduce the risk of probably no solution for solving the problem of formulation based on optimization technique, the conceptual design method and model of double-base solid propellant formulation based on quality function deployment(QFD) and axiomatic design(AD) were proposed. A modified double-base propellant formulation example was designed by the conceptual design system of formulation. The application effect of the model in the conceptual design system of propellant was showed. Results show that in the conceptual design step of formulation, the formulation to preliminary solve is rquired to basically satisfy the index requirement of formulation functional components and their boundary content to ensure the detailed design (optimization design) of subsequent formulation has solution. In traditional design work of formulation, a new method according to "conceptual design+ detailed design +performance prediction + redesign" can effectively avoid the optimization risk from solution, improve the efficiency of formula design and reduce the cost of formula design.

Abstract:In order to study the ignition operating characteristics of the pasty propellant rocket engine, the burning surface change model of pasty propellant was built, and regression equations of pasty propellant were deduced in each stage. The calculating procedure was programmed and the transient pressure of combustion chamber under different transport pipeline diameter and pasty propellant initial accumulation was calculated. Also, the ignition tests were carried out successfully based on a pasty propellant rocket launch test system, and the ignition characteristics of the rocket engine in each working stage were analyzed. Results show that the data calculated by the procedure are in good agreement with the experimental and the maximum absolute error are 5.7%. When the pasty propellant initial accumulation doubled, the initial pressure peak increases by 42.8%. Under the same condition, as the diameter of the pipeline decreases by 60%, the initial combustion time and residual combustion time decrease by an average of 66.5% and 26.1%. The initial pressure peak can be decreased and stable burning time can be increased by reducing the initial packing quantity of pasty propellant, in addition, the stable burning time can be increased apparently by reducing the diameter of transport pipeline.

Abstract:The weak insulation characteristics of unsymmetric dimethyl hydrazine (UDMH) were improved by means of mixing with the insulating oil, which realized the electrorheological effect of UDMH suspension. The experimental study of UDMH suspension was conducted by an electrorheological test device, and the effects of different electric field intensity and alginic acid medium contents on the electrorheological characteristics of UDMH suspension were analyzed. The results show that, the mass flow rate of suspension decreases with increasing the medium mass fraction within and without electric field, but their variation trend is different.With the increase of the medium mass fraction, the mass flow rate without electric field decreases continuously, while the mass flow rate within electric field tends a fixed value, whose value is affected by the interaction of electric field intensity and medium mass fraction. When the content of alginic acid is 30% and the elctric field intensity is 2 kV·mm^-1, the electrorheological effect for the suspension with 5% UDMH is the best. The content of UDMH has a great influence on the suspension insulation, and the suspension in which UDMH content is less than 15%, can achieve the electrorheological effect.

Abstract:In order to improve the low yield of CL-20 and solve the difficult recovery of the catalyst, perfluorinated (1-methyl-ethane) sulfonic acid was grafted onto pure MCM-41 mesoporous molecular sieves to prepare the catalyst of perfluorosulfonic acid MCM-41 molecular sieve (SA-MCM-41). The catalyst was applied in the nitration of TAIW to CL-20 using N₂O₅/HNO₃. Results show that the catalyst has the typical crystal structure of MCM-41 with average pore size of 3.13 nm and specific surface area of 887.25 m²·g^-1. The optimal reaction condition is catalyst 0.5 g, reaction temperature 65-75 ℃ and reaction time 5h with the highest yield and purity of 93.9% and 98.4%, respectively. The catalyst possesses good stability and is easy to separate from the product. Additionally, it can be reused for five times without any significant loss of catalytic activity under the describe reaction conditions.

Abstract:A novel thermally stable energetic material, 4-amino-2, 6-bis(5-amino-1H-tetrazol)-3, 5-dinitropyridine(ABDP) was first synthesized via two-step reactions of nitration and condensation reaction using 4-amino-2, 6-dichloropyridine as a raw material with a total yield of 36%, and its structure was characterized by nuclear magnetic resonance (NMR), mass spectrum (MS) and elemental analysis. Condensation reaction of 3-amino-1, 2, 4-triazole or 5-amino-1H-tetrazole and 4-amino-2, 6-dichloro-3, 5-dinitropyridine was investigated. Its thermal properties were studied by thermogravimetry(TG) and differential scanning calorimetry(DSC). Results show that similar nucleophilicity occurs at primary amine and secondary amine of 3-amino-1, 2, 4-triazole, but secondary amine in 5-amino-1H-tetrazole has higher nucleophilicity than that of primary amine. ABDP has a thermal decomposition peak at 323 ℃ accompanied with 94% mass loss. The detonation velocity and detonation pressure of 4-amino-2, 6-bis(5-amino-1H-tetrazol)-3, 5-dinitropyridine are predicted by Rothstein's method with the values of 8823 m·s^-1 and 36.72 GPa, respectively.

Abstract:In order to improve the compatibility of HMX to liquid bonding agents, octogen(HMX)/TiO₂ composites with reversible wettability were prepared by electrostatic deposition method and then modified by hexadecyltrimethoxysilane. The morphology, polymorph of HMX/TiO₂ composites and the element content on the surface of HMX/TiO₂ composites were tested by scanning electron microscope (SEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscope, respectively. Results show TiO₂ coating with rough structure is constructed on the surface of HMX. The characteristic peaks of HMX/TiO₂ composites in the XRD spectra are attributed to the β-HMX and anatase TiO₂, and strong Ti2p signal appears on the XPS spectra, which further proves that TiO₂ coates on the surface of HMX. The analysis of thermogravimetry-differential scanning calorimetry (TG-DSC) indicates the phase transition temperature of HMX is increased by 8.4 ℃ after coated by TiO₂, and the TiO₂ coating can improve the thermostability of the HMX particles. The water contact angles of HMX/TiO₂ composites treated by hexadecyltrimethoxylsilane is 160.4°, which achieves superhydrophobicity. More interesting, the water contact angles turns to 0° after ultraviolet radiation for 45min, and reversed to 147.9° after dark storage at 80 ℃ for 17 d. So, reversible transformation of surface wettability of HMX/TiO₂ composites is achieved.

Abstract:The two oxidative systems of Cu²⁺/H₂O₂ and Fe²⁺/H₂O₂ were adopted to degrade unsymmetrialdimethy hydrazine (UDMH) wastewater to study degradation efficiency and mechanism, and the impacts of the four factors: pH value, temperature, time and oxidant dosage on the degradation rate of UDMH wastewater were studied. UV-vis method was applied to analyze the oxidative degradation products of UDMH. The mechanism of oxidative degradation of UDMHwas discussed, and the degradation products of two systems at pH 3, 5, 7, 9 were comprehensive comparative analyzed. Results show that the two factors temperature and oxidant dosage have little effect on the degradation rate of UDMH, but pH has great influences on the degradation rate of UDMH and pH is the main factor controlling the type of degradation products of UDMH. The systems of Cu²⁺/H₂O₂ and Fe²⁺/H₂O₂ have the similar degradation products, which are less produced under acidic condition than alkali and neutral conditions. The system of Cu²⁺/H₂O₂ has a relatively high degradation rate on UDMH but many in-process products under alkali condition, and the system of Fe²⁺/H₂O₂ has high degradation efficiency and few in-process products under acidic condition.

Abstract:

Abstract:

Abstract:

Abstract: